I was poking around the library the other day, and I found a Discovery Channel school dvd called "Roller Coaster Physics". It's about 20 minutes long, but it explains alot about gravity, inertia, friction, and other stuff as they affect coasters. I knew most of it already, but they also discussed g-forces and their effect on riders. Apparently, the limit is 3.5 positive g's in the US. Is it different other places? Anyone else seen this dvd?

From my knowledge, anything over about 3.0 g's starts to cause motion sickness / blackouts in a certain percentage of the population. So coasters are generally limited to about 3.0 g's. Simply put, people don't like them when they're any more than that.

I haven't seen the DVD. But, I have watched a few shows about roller coasters on Discovery, History, and Travel channels. Alas, the loss of cable / satellite has kind of cut my viewing (PBS just doesn't have that many show)._________________-Martin

Actually, there are dozens, if not hundreds of coaster going up to 5 G, en the current record is 6-point-something. It's all a matter of duration, though. 5 G seems to be the standard maximum for many manufacturers...

I could be wrong about this, but there's a difference between instantaneous G's and sustained G's. A fighter pilot can withstand a tremendous amount of instantaneous G's but only 5-7 sustained G's without blacking out.

Yes, instantaneous forces usually doesn't do harm. But, it will still put a huge stress on the heart. What happens is that the increased gravity forces the blood to collect at the "lowest" part, typically the legs and feet. This deprives the brain of the blood it needs. So, the heart is told to pump harder. The sudden loss of pressure in the upper extremities can also loosen the cholesterol plates, causing a stroke.

Pilots black out because their hearts can't keep up with the demand for extended periods. The brain loses too much oxygen and starts to shut down. The flight suits they wear actually help them sustain more forces than a normal person. The suit is pressurized in the legs, preventing the blood from collecting down there.

Now, a normal middle aged, non exercise freak guy like me would just about die on some of the big rides. Mission Space just about took me out the last time on the intense simulator._________________-Martin

The heart can actually take quite a lot if we're talking about acceleration spikes. After all, blood has a weight, meaning inertia. Very short periods of acceleration do not affect the heart and blood system that much. Sitting down on a sofa quite fast is said to result in up to 7 G's, en people have been known to survive car accidents with a spike of dozens of G's